The extreme heat rule drew the roof closed over Rod Laver Arena. A severe momentum swing left the walls closing in on Caroline Wozniacki. Shutout in the opening set, a resurgent Christina McHale won seven of the next eight games and had break points for a 2-0 advantage in the decider.

Casting some concerned glances toward her box, Wozniacki relied on some forward thinking, frenetic scrambling, and familiar grit to reverse course. The No. 10 seed won six of the final seven games to score a 6-0, 1-6, 6-2 victory and reach the third round of the Australian Open for the seventh straight year.

It was a match of wild momentum shifts. Dancing on her toes, Wozniacki won seven straight points to open the match. The Dane’s serve set the tone: She served 81 percent and won 12 of 16 points played on her serve in the first set.

A forehand return down the line gave the former No. 1 the second break and a 4-0 lead. McHale, nervous during the brief, 28-minute opener, mishit a few shots and sailed some others beyond the baseline, committing 16 errors compared to Wozniacki's three.

There’s a certain sense of liberation that can come from getting totally thrashed. The realization that as humiliating as things are, they can’t get much worse, seemed to loosen up McHale, who began to step into the court, dictate play with her forehand, and strike with the confidence of the player who had won two of three prior meetings with Wozniacki. This has been a successful match-up for McHale because she can run with Wozniacki, she can hit the forehand with more sting and sharper angle, and she knows Wozniacki predictably plays her forehand crosscourt.

McHale won all 11 points on her first serve in the second set and punished her forehand, reeling off 20 of 24 points in one stretch to level the match and seize a 1-0 lead in the third set. McHale had double-break point for a 2-0 lead, but could not land a return as Woznicki withstood the pressure.

Throughout the second set, the American effectively slid her first serve out wide on the deuce side, opening the court for her forehand. At 1-all in the decider, Wozniacki was waiting on the wide serve. Her forehand return skimmed the net, drawing an error, and when McHale netted a forehand, Wozniacki had the break and a 2-1 lead.

New coach Thomas Hogstedt has encouraged Wozniacki to attack more, and she complied today, hitting three volleys in a row and finishing with a full-stretch forehand stab before blocking a backhand volley to consolidate for 3-1. Wozniacki, whose two-handed backhand volley recalls Nikolay Davydenko, won 11 of 15 net points, including six of seven in the decider. When McHale dumped a double fault into the middle of the net, donating serve to fall into a 1-4 third-set hole, she never recovered.

“The second set didn’t go my way. I was trying to push and play fast, but I was making too many errors,” Wozniacki told ESPN’s Tom Rinaldi. “In the third set, I just kept fighting.”